Difference between revisions of "The longest chord passes through the centre of the circle"

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Investigating the diameter is the longest chord of a circle.
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= Concept Map =
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===Objectives===
__FORCETOC__
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To understand longest chord passes through the centre and it is the diameter
<mm>[[circles_and_lines.mm|flash]]</mm>
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===Estimated Time===
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30 minutes
  
= Textbook =
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===Prerequisites/Instructions, prior preparations, if any===
To add textbook links, please follow these instructions to:
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Prior knowledge of point, lines, angles, polygons
([{{fullurl:{{FULLPAGENAME}}/textbook|action=edit}} Click to create the subpage])
 
  
=Additional Information=
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===Materials/ Resources needed===
==Useful websites==
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* Digital : Computer, geogebra application, projector.
#[http://www.regentsprep.org/Regents/math/geometry/GP14/PracCircleSegments.htm www.regentsprep.com] conatins good objective problems on chords and secants <br>
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* Non digital : Worksheet and pencil, compass, strings
#[http://www.mathwarehouse.com/geometry/circle/tangents-secants-arcs-angles.php www.mathwarehouse.com] contains good content on circles for different classes<br>
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* Geogebra files :  [https://ggbm.at/c4eg7q2u Diameter is longest chord.ggb]
#[http://staff.argyll.epsb.ca/jreed/math20p/circles/tangent.htm staff.argyll]  contains good simulations
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{{Geogebra|c4eg7q2u}}
  
==Reference Books==
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===Process (How to do the activity)===
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Use the geogebra file to show how diameter is the longest chord.
  
= Teaching Outlines =
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Move the points on the circle to show the changes in the triangle.
Chord and its related theorems
 
==Concept #1 Chord==
 
===Learning objectives===
 
# Meaning of circle and chord.
 
# Method to measure the perpendicular distance of the chord from the centre of the circle.
 
# Properties of chord.
 
# Able to relate chord properties to find unknown measures in a circle.
 
# Apply chord properties for proof of further theorems in circles.
 
# Understand the meaning of congruent chords.
 
===Notes for teachers===
 
# A chord is a straight line joining 2 points on the circumference of a circle.
 
# Chords within a circle can be related in many ways.
 
# The theorems that involve chords of a circle are :
 
* Perpendicular bisector of a chord passes through the center of a circle.
 
* Congruent chords are equidistant from the center of a circle.
 
* If two chords in a circle are congruent, then their intercepted arcs are congruent.
 
* If two chords in a circle are congruent, then they determine two central angles that are congruent.
 
  
===Activities===
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What is the condition with respect to sides for formation of a triangle. Sum of two sides is larger than the third side.
#Activity No 1 - [[Circles_and_lines_activity_1|Theorem 1: Perpendicular bisector of a chord passes through the center of a circle]]
 
#Activity No 2 - [[Circles_and_lines_activity_2|Theorem 2.Congruent chords are equidistant from the center of a circle]]
 
  
==Concept #2.Secant and Tangent==
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Compare the chord length with sum of two radii. When is the triangle reduced to a line segment.
===Learning objectives===
 
# The secant is a line passing through a circle touching it at any two points on the circumference.
 
# A tangent is a line toucing the circle at only one point on the circumference.
 
===Notes for teachers===
 
===Activities===
 
#Activity #1 - [[Circles_and_lines_activity_3|Understanding secant and tangent using Geogebra]]
 
  
==Concept #3 Construction of tangents==
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What can you conclude about the chord? When is it the largest?
===Learning objectives===
 
# The students should know that tangent is a straight line touching the circle at one and only point.
 
# They should understand that a tangent is perpendicular to the radius of the circle.
 
# The construction protocol of a tangent.
 
# Constructing a tangent to a point on the circle.
 
# Constructing tangents to a circle from external point at a given distance.
 
# A tangent that is common to two circles is called a common tangent.
 
# A common tangent with both centres on the same side of the tangent is called a direct common tangent.
 
# A common tangent with both centres on either side of the tangent is called a transverse common tangent.
 
  
===Notes for teachers===
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[[Category:Circles]]
===Activities===
 
#Activity #1 - Construction of Direct common tangent
 
#Activity #2 - Construction of Transverse common tangent===
 
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*Estimated Time: 45 minutes
 
*Materials/ Resources needed:
 
# Laptop, geogebra file, projector and a pointer.
 
# Students' individual construction materials.
 
*Prerequisites/Instructions, if any
 
# The students should have prior knowledge of a circle , tangent and direct and transverse common tangents .
 
# They should understand that a tangent is always perpendicular to the radius of the circle.
 
# They should know construction of a tangent to a given point.
 
# If the same straight line is a tangent to two or more circles, then it is called a common tangent.
 
# If the centres of the circles lie on opposite side of the common tangent, then the tangent is called a transverse common tangent.
 
# Note: In general,
 
*The two circles are named as C1 and C2
 
* The distance between the centre of two circles is 'd'
 
* Radius of one circle is taken as 'R' and other as 'r'
 
* The length of tangent is 't'
 
*Multimedia resources: Laptop
 
*Website interactives/ links/ / Geogebra Applets
 
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enableRightClick="false" showAlgebraInput="false" enableShiftDragZoom="true" showMenuBar="false" showToolBar="false" showToolBarHelp="true" enableLabelDrags="false" showResetIcon="true" />
 
*Process:
 
# The teacher can explain the step by step construction of Transverse common tangent.
 
Developmental Questions
 
# What is a transverse common tangent ?
 
# What is the radius of the third circle ?
 
# What is the difference in finding the radius of the third circle in constructing Dct and that of Tct ?
 
# Why was a third circle constructed ?
 
# Let us try to construct transverse common tangent without the third circle and see.
 
# Name the transverse common tangents .
 
# At what points is the tangent touching the circles ?
 
*Evaluation:
 
# Is the student able to comprehend the sequence of steps in constructing the tangent.
 
# Is the student able to identify error areas while constructing ?
 
# Is the student observing that the angle between the tangent and radius at the point of intersection is 90º ?
 
# Is the student able to understand the difference in the construction protocol between direct common tangent and transverse common tangent ?
 
*Question Corner:# What do you think are the applications of tangent constructions ?
 
# What is the formula to find the length of transverse common tangent ?
 
# Can a direct common tangent be drawn to two circles one inside the other ? 
 
# What are properties of transverse common tangents ?
 
*Evaluation:
 
# Were the students able to comprehend the steps in transverse common tangent construction ?
 
*Question Corner:
 
# Can you construct a transverse common tangent without the third circle ?
 
 
 
==Concept # Cyclic quadrilateral==
 
===Learning objectives===
 
# A quadrilateral ABCD is called cyclic if all four vertices of it lie on a circle.
 
# In a cyclic quadrilateral the sum of opposite interior angles is 180 degrees.
 
# If the sum of a pair of opposite angles of a quadrilateral is 180, the quadrilateral is cyclic.
 
# In a cyclic quadrilateral the exterior angle is equal to interior opposite angle
 
===Notes for teachers===
 
===Activity#1. Cyclic quadrilateral ===                                                                                                             
 
*Estimated Time 10 minutes
 
*Materials/ Resources needed: Laptop, geogebra file, projector and a pointer.
 
*Prerequisites/Instructions, if any
 
# Circles and quadrilaterals should have been covered.
 
*Multimedia resources : Laptop
 
*Website interactives/ links/ / Geogebra Applets; This geogebra file was created by ITfC-Edu-Team.
 
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enableRightClick="false" showAlgebraInput="false" enableShiftDragZoom="true" showMenuBar="false" showToolBar="false" showToolBarHelp="true" enableLabelDrags="false" showResetIcon="true" />
 
*Process:
 
# Show the geogebra file.
 
# Move points, the vertices of the quadrilateral and let the students observe the sum of opposite interior angles.
 
Developmental Questions:
 
# What two figures do you see in the figure ?
 
# Name the vertices of the quadrilateral.
 
# Where are all the 4 vertices situated ?
 
# Name the opposite interior angles of the quadrilateral.
 
# What do you observe about them.
 
*Evaluation:
 
# Compare the cyclic quadrilateral to circumcircle.
 
*Question Corner
 
# Name this special quadrilateral.
 
 
 
===Activity No # 2.Properties of a Cyclic quadrilateral===                                                                                                         
 
*Estimated Time: 45 minutes
 
*Materials/ Resources needed
 
coloured paper, pair if scissors, sketch pen, carbon paper, geometry box
 
*Prerequisites/Instructions, if any
 
# Circles and quadrilaterals should have been covered.
 
*Multimedia resources
 
*Website interactives/ links/ / Geogebra Applets
 
This activity has been taken from the website http://mykhmsmathclass.blogspot.in/2007/11/class-ix-activity-16.html
 
*Process:
 
Note: Refer the above geogebra file to understand the below mentioned labelling.,br>
 
# Draw a circle of any radius on a coloured paper and cut it.
 
# Paste the circle cut out on a rectangular sheet of paper.
 
# By paper folding get chords AB, BC, CD and DA in order.
 
# Draw AB, BC, CD & DA. A cyclic quadrilateral ABCD is obtained.
 
# Make a replica of cyclic quadrilateral ABCD using carbon paper.
 
# Cut the replica into 4 parts such that each part contains one angle .
 
# Draw a straight line on a paper.
 
# Place angle BAD and angle BCD adjacent to each other on the straight line.Write the observation.
 
# Place angle ABC and angle ADC adjacent to each other on the straight line . Write the observation.
 
# Produce AB to form a ray AE such that exterior angle CBE is formed.
 
# Make a replica of angle ADC and place it on angle CBE . Write the observation.
 
Developmental Questions:
 
# How do you take radius ?
 
# What is the circumference ?
 
# What is a chord ?
 
# What is a quadrilateral ?
 
# Where are all four vertices of a quadrilateral located ?
 
# What part are we trying to cut and compare ?
 
# What can you infer ?
 
*Evaluation:
 
# Angle BAD and angle BCD, when placed adjacent to each other on a straight line, completely cover the straight angle.What does this mean ?
 
# Angle ABC and angle ADC, when placed adjacent to each other on a straight line, completely cover the straight angle.What can you conclude ?
 
# Compare angle ADC with angle CBE.
 
*Question Corner:
 
Name the two properties of cyclic quarilaterals.
 
 
 
= Hints for difficult problems =
 
#Tangents AP and AQ are drawn to circle with centre O, from an external point A. Prove that  ∠PAQ=2.∠ OPQ
 
Please click [http://karnatakaeducation.org.in/KOER/en/index.php/Class10_circles_tangents#Problem_1 here] for solution.
 
 
 
[[Class10_circles_tangents|here]]
 
 
 
= Project Ideas =
 
 
 
= Math Fun =
 
 
 
'''Usage'''
 
 
 
Create a new page and type <nowiki>{{subst:Math-Content}}</nowiki> to use this template
 

Latest revision as of 16:17, 4 November 2019

Investigating the diameter is the longest chord of a circle.

Objectives

To understand longest chord passes through the centre and it is the diameter

Estimated Time

30 minutes

Prerequisites/Instructions, prior preparations, if any

Prior knowledge of point, lines, angles, polygons

Materials/ Resources needed

  • Digital : Computer, geogebra application, projector.
  • Non digital : Worksheet and pencil, compass, strings
  • Geogebra files : Diameter is longest chord.ggb


Download this geogebra file from this link.


Process (How to do the activity)

Use the geogebra file to show how diameter is the longest chord.

Move the points on the circle to show the changes in the triangle.

What is the condition with respect to sides for formation of a triangle. Sum of two sides is larger than the third side.

Compare the chord length with sum of two radii. When is the triangle reduced to a line segment.

What can you conclude about the chord? When is it the largest?